Conventional alkaline electrochemical cells have an anode comprising zinc and a cathode comprising manganese dioxide. The cell is typically formed of a cylindrical outer housing (casing). The fresh cell has an open circuit voltage (EMF) of about 1.5 volt and typical average running voltage of between about 1.0 to 1.2 Volt in medium drain service (100 to 300 milliamp.) The cylindrical housing is initially formed with an enlarged open end and opposing closed end. After the cell contents are supplied, an end cap with insulating plug is inserted into the open end to form the negative terminal. The cell's open end is closed by crimping the housing edge over an edge of the insulating plug and radially compressing the housing around the insulating plug to provide a tight seal. A portion of the cell housing at the opposing closed end forms the positive terminal.
Primary alkaline electrochemical cells typically include a zinc anode active material, an alkaline electrolyte, a manganese dioxide cathode active material, and an electrolyte permeable separator film, typically of cellulose or cellulosic and polyvinylalcohol fibers. The anode active material can include for example, zinc particles admixed with conventional gelling agents, such as sodium carboxymethyl cellulose or the sodium salt of an acrylic acid copolymer, and an electrolyte. The gelling agent serves to suspend the zinc particles and to maintain them in contact with one another. Typically, a conductive metal nail inserted into the anode active material serves as the anode current collector, which is electrically connected to the negative terminal end cap. The electrolyte can be an aqueous solution of an alkali metal hydroxide for example, potassium hydroxide, sodium hydroxide or lithium hydroxide. The cathode typically includes particulate manganese dioxide as the electrochemically active material admixed with an electrically conductive additive, typically graphite material, to enhance electrical conductivity. Optionally, small amount of polymeric binders, for example polyethylene binder and other additives, such as titanium-containing compounds can be added to the cathode.
The manganese dioxide used in the cathode is preferably electrolytic manganese dioxide (EMD) which is made by direct electrolysis of a bath of manganese sulfate and sulfuric acid. The EMD is desirable, since it has a high density and high purity. The electrical conductivity (resistivity) of EMD is fairly low. An electrically conductive material is added to the cathode mixture to improve the electric conductivity between individual manganese dioxide particles. Such electrically conductive additive also improves electric conductivity between the manganese dioxide particles and the cell housing, which also serves as cathode current collector in conventional cylindrical alkaline cells. Suitable electrically conductive additives can include, for example, graphite, graphitic matererial, conductive carbon powders, such as carbon blacks, including acetylene blacks. Preferably the conductive material comprises flaky crystalline natural graphite, or flaky crystalline synthetic graphite, including expanded or exfoliated graphite or graphitic carbon nanofibers and mixtures thereof.
There are small size rectangular shaped rechargeable batteries now available, which are used to power small electronic devices such as MP3 audio players and mini disk (MD) players. These batteries are typically in the shape of a small cuboid (rectangular parallelepiped) somewhat the size of a pack of chewing gum. Such batteries, for example, can be in the form of replaceable rechargeable nickel metal hydride (NiMH) size F6 or 7/5F6 size cuboids in accordance with the standard size for such batteries as set forth by the International Electrotechnical Commission (IEC). The F6 size has a thickness of 6.1 mm, width of 17.3 mm and length of 35.7 mm. There is a version of the F6 size wherein the length can be as great as about 48.0 mm. The 7/5F6 size has thickness of 6.1 mm, width of 17.3 mm, and length of 67.3 mm. According to the IEC standard allowed deviation for the 7/5F6 size in thickness is +0 mm, −0.7 mm, in width is +0 mm, −1 mm, and in length is +0, −1.5 mm. The average running voltage of the F6 or 7/5F6 NiMH rechargeable batteries when used to power miniature MP3 audio or mini disk (MD) players is between about 1.1 and 1.4 volt typically about 1.12 volt
When used to power the mini disk (MD) player the battery is drained at a rate of between about 200 and 250 milliAmp. When used to power an MP3 player the battery is drained typically at a rate of about 100 milliAmp.
It would be desirable to have a small flat alkaline battery of the same size and shape as small size cuboid shaped (rectangular parallelepiped) nickel metal hydride batteries, so that the small alkaline size battery can be used interchangeably with the nickel metal hydride battery to power small electronic devices such as mini disk or MP3 players.
It would be desirable to use a primary (nonrechargeble) alkaline battery as a replacement for small rectangular shaped rechargeable batteries, particularly small size nickel metal hydride rechargeable battery.